The technique used by Auger and TA to determine the mass composition of UHECR is based on the measurement of the depth \(X_{max}\)  in the atmosphere at which the number of particles in the EAS reaches its maximum and the relative primary particle energy. These measurements are obtained by the FD observation. While in the case of Auger, thanks to enough statistics, the \(X_{max}\)  determination is obtained independently of detector effects, in the case of TA it is impossible, due to the reduced statistics, and the detector effects should be properly subtracted to compare with Auger results (see [1]}, [2]} and references therein).
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